The failure to detect, find and correct minor roof deterioration in the earliest stages is considered the greatest cause of premature roof failure. This is particularly true of roofing materials applied on low-slope or flat roofs. Costly roofing problems are often the result of design deficiencies or faulty application of the roof system, Even when properly designed and applied, all roofing materials deteriorate from contraction and expansion of roof decks and natural aging processes.
Several methods have been used to try and locate roof leaks after they have occurred. Electric capacitance meters identify leaks using a low-frequency that measures dielectric constant changes in the roofing material as a result of moisture below the membrane. Infrared cameras allow technicians to scan roof surfaces for temperature differentials that signify moist areas through changes in thermal conductivity or evaporation. Electric field vector mapping uses a wire loop around the perimeter of the roof surface to introduce an electric potential between the structural deck and a selected roof area which is sprayed with water. The electric field potential caused by a conductive path to any roof membrane damage is then located using a sensitive voltmeter and a pair of probes.
U.S. Pat. No. 4,565,965 issued Jan. 21, 1986 to Geesen discloses an arrangement for detecting leaks in flat roofs in which electrical pulses are transmitted through the moisture in the leak to the roof edge and then the roof is scanned by a pulse sensor and hand-held probe rods to find the leak by locating the maximum amplitude.
The method as described by Geesen requires considerable experience and careful placement of a wire loop around the perimeter of the area to be tested. In particular, metal roof stacks and drains must be isolated by placing secondary loops around them to avoid false readings pointing towards these penetrations.
More recently a scanning platform is described by Vokey in CDN patent 2,613,308 and U.S. Pat. No. 7,554,345 whereby two independent sweep brushes in contact with the surface of the membrane being tested for breaches which penetrate membrane provides a more reliable result.
In all of the above described methods the membranes being tested are required to be electrical insulators. However membranes manufactured using a carbon black component such as ethylene propylene diene monomer (EPDM) or cold applied membranes which contain moisture during a curing process often exhibit a level of conductivity which causes false positives or grounding conditions that invalidates the test.
As described in U.S. Pat. Nos. 2,613,308 and 7,554,345, the outer sweep provides electrical isolation of the inner sweep from external grounds, however the degree of isolation is not sufficient to overcome the grounding effects of membranes which have a moderate level of conductivity.